Which of the following pairs of substances cannot exist together in a solution?

The dissociation constant of acetic acid is $1.6 \times 10^{-5}$ and $\Lambda _{CH_3COOH}^o = 370.6 \times 10^{-4} \, S \, m^2 \, mol^{-1}$. The specific conductance of $0.01 \, M$ acetic acid solution will be approximately:

For a $C \ M$ solution of a weak base $BOH$ having a van't Hoff factor '$i$',the base dissociation constant $K_b$ will be:

At $25^{\circ}C$, $20.0 \ mL$ of $0.2 \ M$ weak monoprotic acid $HX$ is titrated against $0.2 \ M$ $NaOH$. The $pH$ of the solution $(a)$ at the start of the titration (when $NaOH$ has not been added) and $(b)$ when $10 \ mL$ of $NaOH$ is added respectively, are:
Given: $K_a = 5 \times 10^{-4}, pK_a = 3.3, \alpha << 1$

The increasing order of $pH$ of $0.1 \ M$ solution of the following compounds is:

If equivalent conductance of $1 \ M$ benzoic acid is $12.8 \ \Omega^{-1} \ cm^2 \ eq^{-1}$ and if the equivalent conductances of benzoate ion and $H^+$ ion at infinite dilution are $42$ and $288.42 \ \Omega^{-1} \ cm^2 \ eq^{-1}$ respectively,then its degree of dissociation is ............ $\%$